Compared to some of the subjects of author Bruce Hallenbeck's previous books, most notably The Hammer Vampire and The Hammer Frankenstein, The Amicus Anthology likely provided a greater challenge -- one that he thankfully rises to.
For the Hammer Frankenstein films, excepting the one-off spoof/parody Horror of Frankenstein, are unified by the constant presence of Peter Cushing in the title role and, barring The Evil of Frankenstein, Terence Fisher as director/auteur. The Amicus anthology films, by contrast, were directed by Freddie Francis and Roy Ward Baker in approximately equal numbers and had no recurring characters.
The history of Amicus is intrinsically linked to that of its rival. Milton Subotsky presented Hammer with a script for a Frankenstein film. Hammer's bosses didn't like it, but learned that Mary Shelley's characters were out of copyright and thus made their own treatment. This became the epochal Curse of Frankenstein.
Subotsky and other Amicus mainman Max Rosenberg responded to Hammer by employing Christopher Lee for the atmospheric City of the Dead. While not an official Amicus film its present-day setting would emerge as something differentiating Amicus and Hammer horror on aggregate.
There are, in my opinion, three key reasons why The Amicus Anthology works.
First, Hallenbeck provides historical context to the horror compendium film in his opening and closing chapters, which reference the likes of Waxworks, Dead of Night, and Creepshow.
Second, he contextualises Amicus's anthologies in relation to their single-story horrors, such as The Skull, and their non-horror films, such as the Amicus in all but name Dr Who adaptations with Cushing as (a) Who. (This Amicus/Who nexus is worth noting, with third and fourth Who's Jon Pertwee and Tom Baker both appearing in Amicus anthology horrors.)
Finally, Hallenbeck makes you think: Do you prefer to see Amicus's guest stars or Hammer's character actors? Do you prefer segments or wholes? Do you prefer humour as punchline or intermittently? Does a great segment outweigh a good film?